A voltage control device of a vehicular alternator generally includes a circuit board on which a control circuit IC chip and a transistor are mounted, a radiating fin joined to the circuit board with a high thermal conductive adhesive and a case forming a male connector. The radiating fin has various shapes in accordance with such as a use environment and a flow of cooling air.
For example, in a voltage control device disclosed in JP-8-85402, a radiating fin includes a plurality of ribbed protrusions. Each protrusion has a straight wall continuous in an airflow direction. The protrusions are arranged parallel in the airflow direction. In the radiating fin, if foreign materials, such as dust and mud, are caught between the ribbed protrusions, air passages are likely to be blocked. This causes cooling performance degradation.
In a case that a radiating fin is made by pressing to improve manufacturability, ribbed protrusions are formed by being cut and raised up from a base wall of the radiating fin. Therefore, apertures are formed on the base wall. When the base wall is bonded to the circuit board, the adhesive is likely to flow through the apertures and make films between the ribbed protrusions by surface tension. As a result, air passages are blocked, thereby lessening cooling capability.